1. Field of Invention
The present invention relates to a device and method for balancing charge between a plurality of storage batteries, and more specifically, to a low-loss battery balancing system that may be implemented, for example, in a low-power battery balancing application.
2. Background
Electronic monitoring and control applications require continuously supplied power from one or more reliable sources. These sources may generate power (e.g., solar cells, fossil fuel engines, hydroelectric, etc.) or may provide stored power when generated power is not available. If power is supplied from a combination of sources, the flow of energy supplied from these sources must be managed seamlessly. Power spikes or losses often risk an unrecoverable loss of system control, resulting in damage to equipment or possibly life-threatening situations.
Storage batteries are often used as back-up power when generated power is not available. The individual cells of some types of batteries, for example Lithium Ion batteries, may become unbalanced over continuous use. While these batteries may continue to function, the cell unbalancing may cause performance problems and lessen the overall lifespan of the battery. As a result, battery balancing systems are often employed to equalize the energy stored in the battery cells so that performance may be maximized.
Problems may occur, however, as state of the art battery balancing systems age. Analog components employed in the circuits that monitor and redistribute energy amongst the individual battery cells may experience changes in their overall response time due to age, temperature fluctuations, electromagnetic damage, etc. These circuits are usually designed driven at a constant drive frequency that corresponds to the resonant frequency of the circuit as manufactured. As a result, the “evolving” resonant frequency of the circuit no longer matches the original frequency as the circuit is used, and the overall performance of the circuit declines. The system may further experience disturbances due to non-ideal component behavior intrinsic to the circuit itself. These disturbances may include parasitic resistance that adversely affects the accuracy of cell voltages monitored by a microprocessor coupled to the balancing system, which may in turn impact overall system performance. More specifically, inaccurate measured voltages may result in incorrect control execution, false alarms and possibly even damage to the system.
In addition, while these systems may be widely used in high power energy storage applications, they are not as effective for low power battery management. Inherent losses that may be caused by balancing circuit componentry may defeat any benefit that may be realized in balancing the battery cells. For example, transformers may create losses due to core loss and IR loss resulting from magnetizing current. These losses may be acceptable for larger battery cells, but may create a substantial negative impact in system performance with respect to smaller cells.